For those attempting to send metrics when the user session ends, the MDN recommends to use the visibilitychange event:

  @HostListener('window:visibilitychange')
  onBeforeUnload(): void {
    if (this.document.visibilityState === 'hidden') {
      this.userSessionSpan.end();
    }
  }

https://developer.mozilla.org/en-US/docs/Web/API/Window/pagehide_event